Hardening metals such as steel by quenching operations is well known in the art and is widely practiced. Aqueous and oil based quenchants are both commonly used. The quenchants rapidly remove heat from hot metals and in doing so capture a desired microstructure. Control of the quenching process is used to obtain metal products having particular physical properties.
Aqueous based quenching fluids are widely used in industry. They offer the swiftest rates of heat removal but this may be disadvantageous particularly for use with certain alloys or with pieces of thin cross section in that it may cause stress cracking in the metal product. Hydrocarbon based quench oils offer a slower rate of cooling and are also widely used. However, as naturally derived products the composition of such oils may vary and this can introduce significant variations in their performance as a quench oil. In addition they are flammable and their use may pose a fire hazard.
Typical hydrocarbon quench oils are derived from the distillation of petroleum oil and are similar to the base oils used in engine and industrial lubricants. They are complex mixtures of paraffinic and napthenic hydrocarbons as well as oxygenated, nitrogenated and sulphurated derivatives thereof. Quench oil performance can be modified by the introduction of additives that improve wettability or cooling rates or oil stability life and deposit forming tendencies.
U.S. Pat. No. 4,969,959 describes a method for enhancing the thermal quenching of a metal surface which comprises treating the surface with a solution or an emulsion containing a minor proportion of an acid phosphate ester.
U.S. Pat. No. 3,729,417 discloses mineral oil based quenching compositions which comprise a minor proportion of various additives, one class of which are the trialkyl and triaryl phosphate esters. U.S. Pat. No. 4,593,745 discloses processes for continuously casting light metal alloys especially lithium aluminum alloys which utilise organic coolants which coolants may be glycols, mineral oils or phosphate esters. The preferred coolant is ethylene glycol.